Gamma voltage generating circuit functions as to, in accordance with a gamma curve required by a thin film transistor liquid crystal display (TFT-LCD), set gamma voltages as voltages for gray scale display of the TFT-LCD. Each gamma voltage generates all the gray scale voltages under the effect of a digital-to-analog converter of a source driver.
Currently, for the LCD, the gamma voltage generating circuit is usually provided in a source driver IC, and generates the desired respective gamma voltage by adopting voltage dividing resistors. Eight (V1, V2, . . . , V7, V8) or fourteen (V1, V2, . . . , V13, V14) voltage nodes are extracted and those voltages are applied to an external output as shown in FIGS. 1 and 2. FIG. 1 shows the main structure of the source driver IC, which includes the gamma voltage generating circuit, a gamma lookup table, and the source driver.
A relatively large amount of resistors are required to achieve such a gamma voltage generating circuit. For instance, a 6-bit source driver IC needs 129 resistors, and an 8-bit source driver IC needs 257 resistors. These resistors will occupy large space of the source driver IC. In addition, the number of the gamma voltages needs to be increases so as to improve the gray scale display properties of the LCD. Correspondingly, it needs more resistors to constitute the existing gamma voltage generating circuit so as to generate the desired number of gamma voltages. As a result, it is adverse to the integration of the source driver IC, as well as the reduction of the process complexity and the cost.